msm: kgsl: Add support for PDC register subsections

KGSL is required to program two subsections inside the PDC register
block. Map and write only the subsections that KGSL needs to program.
Use the GPU subsections definitions if they are present in the DT.
Otherwise try to determine the GPU subsections from the base
of the PDC register block.

Change-Id: I0ddc8748e497b74da5554ed70dd3179f5f11b4b3
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>